Magnetic phase diagram of the solid solution LaMn 2 (Ge 1− x Si x ) 2 (0 ≤ x ≤ 1) unraveled by powder neutron diffraction

The structural and magnetic properties of the ThCr 2 Si 2 -type solid solution LaMn 2 (Ge 1− x Si x ) 2 ( x = 0.0 to 1.0) have been investigated employing a combination of X-ray diffraction, magnetization and neutron diffraction measurements, which allowed establishing a magnetic composition-temperature phase diagram. Substitution of Ge by Si leads to a compression of the unit cell, which affects the magnetic exchange interactions. In particular, the magnetic structure of LaMn 2 (Ge 1− x Si x ) 2 is strongly affected by the unit cell parameter c , which is related to the distance between adjacent Mn layers. Commensurate antiferromagnetic layers and a canted ferromagnetic structure dominate the Si-rich part of the solid solution, whilst an incommensurate antiferromagnetic flat spiral and a conical magnetic structure are observed in the Si-poor part.